Power supplies of one sort or another are ubiquitous in our technology-driven world. Perhaps the best known portable power supply are batteries, of which there are many types and kinds. Batteries are very versatile power supplies in that they are typically able to power several times their optimum load for short periods of time. Indeed, the average lifespan of a battery is largely dependent upon the duration of its use, in combination with the size of the load applied thereto.
Rechargeable batteries are also known, and they differ only slightly from conventional non-rechargeable batteries in that they may be periodically re-energized via external sources.
Despite their inherent versatility, batteries (both primary batteries, as well as rechargeable batteries) have a limited lifetime and usefulness, and must be replaced or recharged periodically. Thus, operators of high-load electronic equipment often carry several back-up batteries to address the extended operation of their equipment.
Fuel cells are also known power supplies, and are able to produce electrical power from the interaction of a fuel stream, typically consisting of hydrogen gas or the like, and an oxidant stream that contains oxygen. Other types of fuel cells, utilizing different fuel and oxidant streams, are also known.
Practical applications for fuel cells have largely focused on large-scale uses such as stand-by power systems, and automobiles. This is due to the volumetric inefficiencies of fuel cell power plants, which are typically large in size. Thus, fuel cells are not currently considered as viable power supplies for widescale application for small scale electronic devices and appliances.
Moreover, fuel cells are typically designed within demanding parameters. That is, fuel cells are designed to address specific size, weight and performance criteria. In contrast with batteries, fuel cells are able to provide power only marginally above their nominal level, and then for only short durations. If asked to exceed their nominal power output, fuel cells exhibit the characteristic of constant power supplies in that they will typically reduce their voltage output in accordance with Watt's law, addressing a higher current demand by supplying a corresponding lower voltage until such a time that the voltage is no longer capable of powering the load/electronic device.
For this reason, especially when fuel cells are utilized in automobile applications, batteries are employed as the primary power source for the nominal load and in order to address the transient peak loads that the fuel cell alone would otherwise be unable to handle. Such battery complimented fuel cell systems are often termed ‘hybrid’ systems.
Other, somewhat smaller, hybrid power systems have been proposed, yet the operation of the batteries in these systems has been limited to merely assisting in the requisite temperature rise necessary to start the chemical reaction within the fuel cell itself. Batteries in hybrid systems have also been employed to provide some capacitance by which to insulate the fuel cell from transient currents, thereby allowing the voltage output from the hybrid system to remain substantially constant.
Still further, the batteries utilized in known hybrid power systems are integral to the fuel cell construction, and have not been designed to handle the nominal load placed on the fuel cell. Thus, known hybrid systems utilize their integral batteries to merely assist the fuel cell, which itself is the main power supply for the electrical device.
Known fuel cell hybrid power systems also suffer from being a ‘closed’ power system. That is, known hybrid power systems are only designed to address the power demands of a specific type of electric device, and most commonly are designed to address the power demands of a single, individual unit within the specific type of electric device. Thus, known hybrid power systems are not capable of powering even other units within the specific type of electrical device, and are certainly incapable of being mounted to and servicing the power demands of a wide variety of electric devices.
Automotive hybrid power systems are but one example of a closed power system in that they are only designed for a specific type of electric device (an automobile), and are only useable with a single vehicle. The hybrid power system of one vehicle cannot be simply disconnected and mounted to the chassis of another vehicle without extensive labor and expense. Moreover, the hybrid power system of a vehicle certainly cannot be mounted or connected to a different type of an electric host device, such as a video camera or the like.
In spite of the limitations discussed above, there are conceivably a wide range of products that would benefit from the use of fuel cells as a power supply. For example, in those applications where the electrical device is operated for extended periods of time away from a landed AC power source, it is often necessary to carry large amounts, and differing kinds, of batteries and/or associated recharging devices. One benefit of fuel cells, despite their volumetric inefficiency, is that the fuel itself (apart from its converter apparatus) can be carried in relatively smaller and lighter containers versus carrying the equivalent power in batteries.
Batteries, however, remain the power supply of choice in many fields, including, by way of illustration and example, that of professional camera and video operators. In the professional video art, a video camera may be used in different environments, by different operators and for different durations. A selection of battery sizes, chemistries and capabilities will allow the video camera to be used in all of these different situations, wherein the selection of batteries is optimized by the preference of the operator considering the environmental and running time requirements.
As discussed above, the optimization of size, weight and run time is not available to a fuel cell, whose output is largely defined by its size and weight. Moreover, the size and weight of a fuel cell that was designed to handle all operating conditions, would negatively affect the ergonomics of today's camera and video units, which have increasingly become smaller and lighter. Still further, because a fuel cell could be sized to only address a device of certain. characteristics, its flexibility to be used interchangeably in several different devices would be severely limited.
Large scale video operations, such as those employed for news services and the like, could have literally hundreds of cameras. Each camera could range in power requirements from 15-50 watts and have accessories, such as lights, that could add from 25-85 watts per camera. Therefore, the requisite power range in professional video applications such as news gathering (ENG), field productions (EFP), event videography (e.g., weddings) and government or corporate video operations, can range anywhere from 15-150 watts. This 10× power range makes it virtually impossible for a fuel cell of existing technology to universally power this range of device. Moreover, the upper range of the power requirement would necessitate a fuel cell which would be so large and heavy to be ergonomically impractical for the device it would power. Clearly, the application of fuel cells is limited in circumstances where the size and power demands of a wide range of devices, or of a portable device with high current requirements, make the volumetric limitations of fuel cells impractical.
As will be appreciated by a review of the foregoing, neither batteries, nor existing technology fuel cells, can efficiently and fully address the power, space and weight requirements of small-scale electrical appliances and devices on their own. Indeed, even the application of known hybrid designs cannot address these concerns as known hybrid power plant systems approach or exceed the size of small-scale electrical appliances. Moreover, known hybrid systems require the integral coupling between a battery and a fuel cell, thus making replacement of the battery a time consuming and labor intensive act which interrupts the continuous operation of the device. Still further, known fuel cell hybrid power systems are incapable of being selectively applied to a wide variety of electric host devices, instead being limited to use with a very specific type, and most commonly an individual unit, of an electric host device.
With the forgoing problems and concerns in mind, it is the general object of the present invention to provide a dual power supply for portable electronic devices that addresses the shortcomings of both batteries and fuel cells by extending the operating time of the device, while permitting the continuous operation of the device even during times of battery or fuel replacement.